1. Field of the Invention
The present invention relates to a starter provided with a thermostat.
2. Description of the Related Art
A starter is activated by the action of switching on a start switch of a key switch, whereby an engine is ignited and started. Once the engine is ignited and started, the starter is deactivated by the action of switching off the start switch of the key switch. At that time, for reasons such as incomplete return of the key switch, etc., the start switch may not be switched off and the starter may continue to be energized even after the engine has been started, whereby the starter generates heat and is damaged by that heat.
For that reason, in conventional techniques a thermostat is built into the starter to detect the ambient temperature within the starter and terminate operation of the starter if the ambient temperature within the starter exceeds a predetermined temperature in order to prevent excessive continuous energizing of the starter.
Actual examples of such starters include starters with a thermostat built directly into one of the brushes and starters with a thermostat disposed beside one of the brushes.
FIG. 7 is a cross-section showing an example of a starter with a thermostat disposed beside one of the brushes.
In the figure, the shaft 103 of an armature 101 comprising commutator segments 102 disposed plurally around the circumference thereof and constituting a motor portion is supported by a bearing 104 so as to be able to rotate freely. The bearing 104 is inserted into and supported by a recess portion 105a disposed in a thin-walled rear bracket 105 which houses the armature 101.
Brushes 106 which contact the commutator segments 102 and, together with the commutator segments 102, constitute contacts for supplying electric current to the armature 101 are disposed in positions facing the commutator segments 102. Lead wires 110 are connected to the brushes 106. The brushes 106 are pressed against the commutator segments 102 with a predetermined pressure by springs 107 and are supported by brush holders 108. The brush holders 108 are disposed at four positions equidistantly spaced around the circumference of the armature 101 and are secured to a base 109 by rivets (not shown). A female thread is disposed in the base 109, and the base 109 and the rear bracket 105 are secured to each other by inserting a bolt from the outer end surface of the rear bracket 105 into a bore (not shown) disposed in the end of the rear bracket 105 so that the bolt engages the female thread disposed in the base 109. In this way, the brush holders 108 are supported by the rear bracket 105.
The brushes 106 are heated by heat generated by friction between the brushes 106 and the commutator segments 102 and by heat generated by the motor portion of the starter which is conducted to the brushes 106. A long, slender, rod-shaped thermostat 160 for detecting increases in the temperature of the brushes due to brush heat being the heat contained in the brushes 106 and interrupting the energizing of the starter is disposed in the vicinity of the brushes 106 radially outside the brushes 106 relative to the armature 101 such that the longitudinal direction of the thermostat 160 is parallel to the axial direction of the armature 101.
Within the thermostat 160 which comprises a hollow pipe-shaped steel terminal 165 having a closed end, one tip of a lead wire 161 which is one of two lead wires indicated by broken lines in the figure is connected to one end of a bimetallic element 162, and a contact 163 is disposed on the other end of the bimetallic element 162. Another contact 166 is disposed on one tip of the other lead wire 164. The bimetallic element 162 deforms such that above a predetermined temperature the contacts 163, 166 are open and on or below the predetermined temperature the contacts 163, 166 are closed.
The two lead wires 161, 164 lead from the steel terminal 165 to the outside, extending so as to be insulated from each other, and a male terminal 167 is connected to the tip of each of the lead wires 161, 164. A connector 168 is integrally formed by molding resin such that the two lead wires 161, 164 are covered.
An O-ring 169 is disposed on the cylindrical outer circumferential portion 168a of the connector 168. A flat plate-shaped flange 168b extends from the vicinity of the center of the connector 168. The connector 168 which is integrated with the thermostat 160 is secured to the rear bracket 105 by inserting a bolt 115 into a bore 168c disposed in the flange 168b and engaging a female thread 105a disposed in the rear bracket 105.
A hollow cylindrical resin holder 116 having a closed end fits over the steel terminal 165 of the thermostat 160 and is disposed on an outer circumferential portion of the steel terminal 165.
However, in many starters with a thermostat disposed in the vicinity of the brushes, the brush heat is transferred to the thermostat by radiation through air and it takes time for the brush heat to be transferred as far as the thermostat, making the temperature increases in the thermostat slower than the temperature increases in the brushes. For that reason, in some cases the starter may possibly be damaged by heat before the operation of the starter is terminated by the action of the thermostat.
Furthermore, in starters with a thermostat built into one of the brushes, installation of the thermostat is difficult because the thermostat is embedded in the brush, and even if installation is possible the brush has to be enlarged, making the starter larger.
The present invention aims to solve the above problems and an object of the present invention is to provide a compact starter with superior heat transfer efficiency wherein the brush heat is conducted directly to the thermostat by means of a heat conducting member interposed between one of the brushes and the thermostat.
In order to achieve the above object, according to one aspect of the present invention, there is provided an engine starter comprising:
a starter motor for starting an engine, the starter motor including a brush and a brush holder; and
a control circuit for controlling the starter motor, the control circuit including a thermostat for deenergizing the starter motor when the temperature of the starter motor exceeds a predetermined temperature;
the engine starter further comprising:
a heat conducting member, having a first end thermally coupled to the brush and a second end thermally coupled to the thermostat, for conducting heat from the brush to the thermostat.
According to another aspect of the present invention, the thermostat is secured to the heat conducting member and the heat conducting member is a substantially only means for mechanically supporting the thermostat.
According to another aspect of the present invention, the heat conducting member supports the thermostat within the starter motor with a thermally insulating air gap defined therearound.
According to another aspect of the present invention, the heat conducting member is a substantially xe2x80x9cLxe2x80x9d-shaped metal member having first and second legs of xe2x80x9cLxe2x80x9d, the first leg being thermally coupled to and extending from the brush in a substantially radial direction of the starter motor, and the second leg extending in a substantially axial direction of the starter motor and substantially along the thermostat.
According to another aspect of the present invention, the second leg has a bend portion for positioning the thermostat on the second leg.
According to another aspect of the present invention, the thermostat and the second leg of the heat conducting member are wrapped together by an adhesive tape.
According to another aspect of the present invention, an electrically insulating material is interposed between the thermostat and the second leg of the heat conducting member.
According to another aspect of the present invention, the first end of the heat conducting member is embedded within the brush.
According to another aspect of the present invention, the first end of the heat conducting member is an integral, continuous extension of the brush holder.
According to another aspect of the present invention, the first end of the heat conducting member extends from a mounting flange of the brush holder.
According to another aspect of the present invention, the first end of the heat conducting member is mechanically fastened to the brush holder.
According to another aspect of the present invention, the first end of the heat conducting member is held between a rear bracket of the starter motor and the brush holder secured to each other.
According to another aspect of the present invention, a thermally insulating material is interposed between the rear bracket and the first end of the heat conducting member.